Fuel Pump

Boomer

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#31
I did an interesting bit of troubleshooting when I got home. I drove home fine. No problems. Pulled in the garage, shut if off. Tried to restart. Cranked fine, no start. Listened for the fuel pump, Key on, engine off. The pump was not running. I inserted a jumper between 87 and 30 and the pump ran fine. This tells me the pump and it's ground are likely ok. If I'm wrong, feel free to advise.

I switched relays with the horn. I made sure the horn honked. I pulled the relay, then verified that it no longer honked. I inserted it into the fuel pump slot and still the pump wouldn't run. I have the constant 12V feed coming to the connector from ECM B. Throughout all of this I tried several times to turn the key and listen for the pump. It wasn't until after approximately 45 minutes that the pump would start running with the key again. This is making me wonder, is it the coil side of the relay wiring having a problem? I've tried a few different relays and I get the same result.

Does anyone think the PCM could be at fault? Thinking this stuff through, what are your thoughts? As always, I appreciate your help.
 
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#32
Am I saying this right? You rotate key to ON position, fuel pump runs briefly. If you crank it, it will start.
BUT SOMETIMES........... You rotate key to ON position, fuel pump does not run briefly. If you crank it, it will not start.
 

Boomer

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#33
Am I saying this right? You rotate key to ON position, fuel pump runs briefly. If you crank it, it will start.
BUT SOMETIMES........... You rotate key to ON position, fuel pump does not run briefly. If you crank it, it will not start.
Yes, after it cools off, fuel pump runs and the truck will start.

When I have driven say.... 16 miles to or from work, as soon as I shut it off, there is no fuel pump run and no start. It took approximately 45 minutes before it would restart after work tonight. HOWEVER, if I connect 87 and 30 in the fuel pump relay contacts with a jumper wire, the fuel pump comes right on even though the key ON, will not fire up the pump.
 
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#34
If you don't hear that one second buzz keeping on switching off the ignition until you do, did this on our S10 for awhile until I got around to looking at it.

Was in my Cruze 40 miles from home, hit the starter, nothing, switched off the ignition and had to open the door on this thing each time. Third time it started, when I got home, pulled the ignition relay, contacts were dirty, but took a couple of closures to get it working again. Cheap relay, replaced it with a Panasonic.

In electronics when warm and not working, could get it working again by spraying CFC's on it, cools it down, contracts and makes better contact to find the bad component.
 
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#36
So...It seems likely that some component "fails hot" but comes back to life after a short time in the grave. Lazarus, Jesus, or the PCM seem like the most likely possibilities. Maybe ignition switch. Maybe too much resistance somewhere in the "relay coil circuit". If you can establish that PCM takes 45 min to revive after 15 min drive at 40 degrees ambient (or some version of that), prep an ice bag (cubes and water in a ziplock) and lay against PCM to see if the recovery time becomes quicker. Am I correct in thinking that your S-10 has the PCM under the hood and icing it would be reasonably easy?
 

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#37
So...It seems likely that some component "fails hot" but comes back to life after a short time in the grave. Lazarus, Jesus, or the PCM seem like the most likely possibilities. Maybe ignition switch. Maybe too much resistance somewhere in the "relay coil circuit". If you can establish that PCM takes 45 min to revive after 15 min drive at 40 degrees ambient (or some version of that), prep an ice bag (cubes and water in a ziplock) and lay against PCM to see if the recovery time becomes quicker. Am I correct in thinking that your S-10 has the PCM under the hood and icing it would be reasonably easy?
It is indeed under the hood sitting on top of the radiator overflow jug. I'm wondering if I didn't cause this somehow while doing the heater core. It started immediately after that. I had the entire dash out. I had to lower the steering column and rest it on a pile of towels on the drivers seat. I also had to pull the inner fender on the passenger side. (which coincidentally has the overflow jug and PCM mounted on it so I had to move those) I did feel the PCM last night and it felt ok. I looked at it's wiring connectors, didn't see anything out of the ordinary.

I was thinking of taking the hush panels off the underneath of the drivers side and doing a good visual inspection of the ignition wiring to make sure it's all tight. Am I correct in thinking the relay coil stays pulled in the whole time the truck is running right? I mean there isn't some other circuit where the PCM takes over after the vehicle has been started?
 

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#38
Did the PCM or its connections get wet with coolant during the heater core job? Pure water doesn't do electrical stuff any good, but it's not a conductor.
 

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#39
Did the PCM or its connections get wet with coolant during the heater core job? Pure water doesn't do electrical stuff any good, but it's not a conductor.
I don't think so. I didn't notice any.
 

billr

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#40
It's a little late, but I gotta ask... do you have spark and injector pulses when the pump won't run? Maybe this is a CKP sensor problem, not the pump at all.
 

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#40
It's a little late, but I gotta ask... do you have spark and injector pulses when the pump won't run? Maybe this is a CKP sensor problem, not the pump at all.
I really don't know Bill. I didn't check that. Wouldn't I have a check engine light if something was wrong with that?
 
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#41
Bill...the "one second fuel pump buzz".....you don't need a good crank sensor to make that happen. When Boomer's truck won't start, the "one second fuel pump buzz" isn't happening.
 

Boomer

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#42
Bill...the "one second fuel pump buzz".....you don't need a good crank sensor to make that happen. When Boomer's truck won't start, the "one second fuel pump buzz" isn't happening.
I "think" I may have found the problem. My troubleshooting telling me that it was the coil side of the relay causing the problem and, what I said in post 37 above about this starting right after the heater core led me to checking things. I actually had a friend at work the other day say "I think you may have caused your own problem doing that core"
I took those hush panels off and noticed my key was no longer making that ding ding sound when it's in the ignition. The horn wasn't working. I checked every fuse with my multimeter and they were all good. I thought ok, the horn, key alarm, coil to relay all comes from the key. I reached in and started moving those wires around and key alarm came back on. Horn still wasn't working. I tilted the wheel down, key alarm quit again. Ok, something is loose. Move the wires again, key alarm comes back. I can see the whole harness goes down to the connector in the picture.

When I was pulling the dash, I thought I had to pull that connector apart because I had to pull the one like it apart on the passenger side. Well guess what? I had left it loose. After tightening it back up, I hit the horn, it worked. I turned the key forward, the fuel pump buzz was there. :)

Now I can't say it's fixed yet because the truth will come after I drive it long enough to get it nice and hot and see what happens but, I'm feeling pretty good about it.
 

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jd

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#43
Always good o go back and re-check recent work... Hopefully this is it.
 

billr

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#44
"Listened for the fuel pump, Key on, engine off. The pump was not running"

That was in reply #31 and had me confused. I thought maybe the "1-sec key-on buzz" was not happening.
 

Boomer

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#45
"Listened for the fuel pump, Key on, engine off. The pump was not running"

That was in reply #31 and had me confused. I thought maybe the "1-sec key-on buzz" was not happening.
That's what happened after it was hot Bill